The present invention relates to a variable displacement compressor having a displacement control valve.
When a variable displacement compressor is at a stop for a long period of time, refrigerant present in the compressor is liquefied, and the liquid refrigerant is stored in a space such as a crank chamber and a suction chamber. In this case, the pressure in the crank chamber is high, so that the inclination of the swash plate disposed in the crank chamber is minimum. Since the pressure in the crank chamber is maintained at a high level at a start of the compressor and the inclination of the swash plate does not become maximum until no liquid refrigerant is present in the crank chamber, a desired cooling performance is not obtained quickly.
Such variable displacement compressor is provided with a bleed passage having therein a flow restrictor of a fixed cross-sectional area that serves to drain liquid refrigerant from the crank chamber into the suction chamber in order to control the displacement of the compressor while the compressor is operating. However, it takes a long time to drain the liquid refrigerant in the crank chamber through the bleed passage at a start of the compressor and, therefore, a desired cooling performance is not obtained quickly.
For example, Japanese Unexamined Patent Application Publication No. 2009-103074 discloses such variable displacement compressor having a displacement control valve that allows quick drain of liquid refrigerant from a control chamber (crank chamber) just after a start of the compressor thereby to shorten the time taken to increase the displacement. When the compressor is at a stop for a long period of time, liquid refrigerant is stored in the control chamber. When the liquid refrigerant stored in the control chamber flows into and fills a pressure-sensing chamber formed in the displacement control valve, a bellows disposed in the pressure-sensing chamber is contracted by the pressure of the liquid refrigerant against the urging force of a spring disposed in the bellows.
As a result, a pressure receiving member connected to the bellows is moved away from a second valve member of the displacement control valve. The liquid refrigerant present in the control chamber is flowed into a drain passage that is opened to the control chamber at a position adjacent to the central axis of the control chamber, and then the liquid refrigerant is drained into the suction chamber through the pressure-sensing chamber, an in-shaft passage, a gap passage, a recessed space and a valve chamber of the displacement control valve and a passage. Since refrigerant present in the discharge chamber is prevented from flowing into the control chamber, the pressure in the control chamber is quickly lowered and the inclination of the swash plate is quickly changed from minimum to maximum without being hampered by liquid refrigerant, so that a desired cooling performance is obtained quickly after a start of the compressor.
The structure disclosed in the above publication No. 2009-103074 does not necessarily shorten sufficiently the time taken to drain the liquid refrigerant in the control chamber. This is because the drain passage connecting the control chamber and the displacement control valve for draining of liquid refrigerant is located at a position adjacent to the central axis of the control chamber, or adjacent to the rotary shaft of the compressor. For example, when the compressor installed on a vehicle is started, the stored liquid refrigerant whose level is above the drain passage is quickly drained through the drain passage toward the suction chamber, but the stored liquid refrigerant whose level is between the drain passage and the bottom of the control chamber is not drained through the drain passage until the liquid refrigerant is evaporated. Thus, it takes a long time to drain the liquid refrigerant completely, and a desired cooling performance is not necessarily obtained quickly after a start of the compressor.
The present invention is directed to providing a variable displacement compressor of a structure that helps to shorten the time taken to drain liquid refrigerant in a crank chamber at a start of the compressor.